1. Field of the Invention
The present invention relates generally to switching power regulator circuits, and more specifically, to a switching power converter in which an auxiliary winding power supply includes a boost circuit to increase available voltage.
2. Background of the Invention
In order to supply power to control circuits of a switching power converter, an auxiliary winding is sometimes used, particularly at start-up when the voltage of the converter output has not risen sufficiently, or in implementations in which deriving an internal low-voltage “auxiliary” power supply from the output or input of the converter is impractical or very inefficient, e.g., in high-voltage input converters. Since the auxiliary power supply typically does not have to source much current, the filter capacitor or LC circuit that removes large AC variations from the output of the auxiliary power supply can be small compared to the output filter of the converter. Therefore, the auxiliary power supply voltage can rise much more rapidly than the output of the converter and is available as a voltage source for control circuits much earlier than the output of the converter itself.
However, even an auxiliary winding-sourced power supply requires time for the filter capacitor or LC circuit that removes large AC variations from the auxiliary power supply output to charge to a sufficient voltage to operate the control circuits. Therefore, there is generally a start-up lag time required, during which converter switching circuits must be operated without the control circuits powered by the auxiliary winding.
Therefore, it would be desirable to provide an auxiliary power supply circuit and method that provide operating voltage for control and/or other circuits earlier in the start-up phase of a switching power regulator.